It is known that 1,4-diamino-2,3-dicyanoanthraquinone can industrially be produced advantageously by reacting an aqueous solution of 1,4-diaminoanthraquinone-2,3-disulfonic acid with a cyan compound according to the known processes (as disclosed in West Germany Pat. No. 935,669, U.S. Pat. No. 3,203,751, Japanese Patent Publication No. 17643/1974, and Japanese Patent Application (OPI) No. 77251/1981). The term "OPI" as used herein refers to a "published unexamined Japanese patent application". It is known that the starting material of this process, 1,4-diaminoanthraquinone-2,3-disulfonic acid, can be produced by heating a 1,4-diamino-2,3-dihalogenoanthraquinone with boric acid in concentrated sulfuric acid to form a borate compound of the 1,4-diamino-2,3-dihalogenoanthraquinone and then heating this borate compound with an alkali metal sulfite in an aqueous medium, according to the known processes (as disclosed in U.S. Pat. Nos. 1,975,386 and 2,795,593, and Japanese Patent Publication No. 2323/1974).
These known processes involve three steps of boration, sulfonation, and cyanogenation of the 1,4-diamino-2,3-dihalogenoanthraquinone, and suffer from the following disadvantages which result from the use of a large amount of sulfuric acid in the first boration step.
(1) The reaction system requires a large amount of a neutralizing agent or a buffering agent before proceeding to the sulfonation step. Moreover, the reaction system requires a large amount of ice or cooling energy for the removal of heat of neutralization. This costs a great deal.
(2) In the sulfonation step, the reaction system is diluted with a large amount of water and contains a large amount of inorganic salts. Therefore, it is not advantageous from the economical viewpoint to proceed the cyanogenation step as it is and hence, it is necessary to isolate the 1,4-diaminoanthraquinone-2,3-disulfonic acid. This isolation step is accompanied by the discharge of waste water containing a large amount of inorganic salts. This is unfavorable for the preservation of the environment.
(3) The borate compound of the 1,4-diamino-2,3-dihalogenoanthraquinone obtained in the first step is very unstable to heat, acid, or alkali under the condition where water is present as in the second step. Thus a certain amount of the borate compound hydrolyzes during the sulfonation and returns to the starting material. As the result, the yield of 1,4-diaminoanthraquinone-2,3-disulfonic acid is not necessarily satisfactory.
According to another known process, the boration is carried out in an organic solvent such as phenol, acetic anhydride, and nitrobenzene. The former two are disclosed in U.S. Pat. No. 1,975,386, and the last one, in Japanese Patent Application (OPI) No. 69553/1980.
The use of phenol causes an unsolved problem of waste water disposal. The use of acetic anhydride is not useful on an industrial scale because it is reported that a mixture of acetic anhydride and boric acid causes explosion (see Chemical & Engineering News, Aug. 20, (1973) p. 42). The last one is not economical because the reaction does not complete unless boric acid is used in large amount (6 to 8 times (in mole) the quantity of starting material). Moreover, these processes have a disadvantage in common that it is necessary to isolate once the borate compound of the 1,4-diamino-2,3-dihalogenoanthraquinone and to recover the used solvent by complex processes.
Thus, the process for using an organic solvent for boration is not satisfactory enough to replace the process for using sulfuric acid and could not completely solve the problem.
In order to overcome the above-mentioned disadvantages, the present inventors carried out a series of studies on the process for converting the halogen atoms in the 1,4-diamino-2,3-dihalogenoanthraquinone directly to the sulfonic groups. As the result, it was unexpectedly found that when the reaction is carried out in an aqueous medium in the presence of at least one of a quaternary ammonium compound and a quaternary phosphonium compound, the 1,4-diamino-2,3-dihalogenoanthraquinone reacts directly with a sulfonating agent such as an alkali metal sulfite to give 1,4-diaminoanthraquinone-2,3-disulfonic acid or a salt thereof. It was also found that when the thus obtained 1,4-diaminoanthraquinone-2,3-disulfonic acid or salt thereof is reacted in succession with a cyanogenation agent without isolation of the 1,4-diaminoanthraquinone-2,3-disulfonic acid or salt thereof, 1,4-diamino-2,3-dicyanoanthraquinone can be obtained easily. The present invention is based on these findings.